Chocolate Semifreddo

Lightly spray loaf pan with vegetable oil spray and line with plastic wrap, leaving 3-inch overhang on all sides. Place chocolate in large heatproof bowl; set fine-mesh strainer over bowl and set aside. Stir vanilla and espresso powder in small bowl until espresso powder is dissolved.

Whisk eggs, sugar, and salt in medium bowl until combined. Heat ½ cup cream (keep remaining 1½ cups chilled) and water in medium saucepan over medium heat until simmering. Slowly whisk hot cream mixture into egg mixture until combined. Return mixture to saucepan and cook over medium-low heat, stirring constantly and scraping bottom of saucepan with rubber spatula, until mixture is very slightly thickened and registers 160 to 165 degrees, about 5 minutes. Do not let mixture simmer.

Immediately pour mixture through strainer set over chocolate. Let mixture stand to melt chocolate, about 5 minutes. Whisk until chocolate is melted and smooth, then whisk in vanilla-espresso mixture. Let chocolate mixture cool completely, about 15 minutes.

Using stand mixer fitted with whisk attachment, beat remaining 1½ cups cream on low speed until bubbles form, about 30 seconds. Increase speed to medium and beat until whisk leaves trail, about 30 seconds. Increase speed to high and continue to beat until nearly doubled in volume and whipped cream forms soft peaks, 30 to 45 seconds longer.

Whisk one-third of whipped cream into chocolate mixture. Using rubber spatula, gently fold remaining whipped cream into chocolate mixture until incorporated and no streaks of whipped cream remain. Transfer mixture to prepared pan and spread evenly with rubber spatula. Fold overhanging plastic over surface. Freeze until firm, at least 6 hours.

When ready to serve, remove plastic from surface and invert pan onto serving plate. Remove plastic and smooth surface with spatula as necessary. Dip slicing knife in very hot water and wipe dry. Slice semifreddo ¾ inch thick, transferring slices to individual plates and dipping and wiping knife after each slice. Serve immediately. (Semifreddo can be wrapped tightly in plastic wrap and frozen for up to 2 weeks.)